Di Gregorio, who has been suspended by his Cofidis team following his arrest Tuesday and has dropped out of the Tour de France, admits receiving injections, but denies any charges of doping.

The 26-year-old French cyclist was arrested following a police raid at his team's hotel in Bourg-en-Bresse outside Macon in eastern France on Tuesday as part of an investigation into the organised trafficking of doping substances.

He was taken to Marseille for further questioning by investigating magistrate Annaick Le Goff, along with two other men, who were suspected of "having dealings" with Di Gregorio.

One of the two other men was released on Wednesday, but a 75-year-old man remained in custody along with Di Gregorio and he is facing charges of "using banned substances or procedures on a sportsman" and "the illegal practice of medicine."

At least four injections were carried out on Di Gregorio between the end of May and the end of June, Dallest said.

Dallest said other people would be questioned as part of the ongoing investigation but it was not a case of everyone at Cofidis being called into question.